ENG-7185: Improve deployment file processing error reporting:
- Replace meaningless -1 return value with actual error message and
  fixup clients
- Capture all exceptional conditions generated by deployment file handling
  and turn them into errors
- Get rid of awkward crashOnValidation pattern for path checking and let
  the caller make the right decision instead
Merge pull request #1860 from VoltDB/eng7185

ENG-7185: Improve deployment file processing error reporting, r=jhugg,scooper
Merge remote-tracking branch 'origin/master' into hugg-noartifactsfromliveddl